Technical Field

[0001] The invention relates generally to wind turbines, and more particularly to hub segments and hub assemblies for connecting a wind turbine blade to a rotor shaft, and a method of forming hub segments and hub assemblies having improved joints for connecting the wind turbine blade to the rotor shaft.

Background

[0002] Wind turbines are used to produce electrical energy using a renewable resource and without combusting a fossil fuel. Generally, a wind turbine converts kinetic energy from the wind into electrical power. A

horizontal-axis wind turbine includes a tower, a nacelle located at the apex of the tower, and a rotor having a central hub and a plurality of blades coupled to the hub and extending outwardly therefrom. The rotor is supported on a shaft extending from the nacelle, which shaft is either directly or indirectly operatively coupled with a generator which is housed inside the nacelle. Consequently, as wind forces the blades to rotate, electrical energy is produced by the generator.

[0003] In recent years, wind power has become a more attractive alternative energy source and the number of wind turbine, wind farms, etc. has significantly increased, both on land and off-shore. Additionally, the size of wind turbines has also significantly increased, with modern wind turbine blades extending from 50 to 80 meters in length. The length of wind turbine blades is expected to further increase in the future. The increased length has introduced a number of interesting design considerations for wind turbine designers and manufacturers. For example, with increasing blade length, the joint between the wind turbine blade and the rotor hub may experience increased stresses. In addition, to ensure that the rotor hub can withstand the expected loads, stronger hubs are required.

[0004] As the stress on the hub is expected to increase, the hub must be made stronger. To that end, the size of the hub may be increased to carry the additional load. Typically, the hub is a one-piece casting. For a one-piece casting, size increases may be problematic for many reasons. For one, the cost may increase dramatically in terms of added material to the hub itself and to the mold necessary to produce a larger hub. Additional costs may include those necessary to address transportation issues because special equipment may be required to transport these massive metallic monoliths from their manufacturing site to their installation site. Moreover, specialized cranes may be required to lift it into position.

[0005] To address these problems, segmented hubs have been contemplated. Segmented hubs may be assembled from separate

components. Thus, each component may be separately manufactured and transported from the manufacturing facility to the installation site. At the installation site, the individual components may be assembled together.

However, even though segmented hubs may address some manufacturing and transportation issues, problems with the load carrying capacity of those hubs remain. The load carrying capacity generally relates to how the separate components are connected. That is, the joints may serve as a weak point in the assembled hub.

[0006] Assembling segmented hubs may include welding where each of the individual components is metallic. Difficulties remain for joining composite components formed from fibrous material and resin. Such materials are generally not weldable in the same way as metals and generally do not have the structural integrity to provide a secure fixing mechanism into which threaded bolts may be directly inserted. A hole or bore, for example, may be tapped into the composite material to provide a complementing thread upon which the threaded bolt may achieve a connection with, for example, an adjacent metallic component or even an adjacent composite component. However, the composite material has insufficient shear strength to transfer the loads between the two components via the bolts and deterioration of the composite material at the interface would occur.

[0007] For this reason, manufacturers attempt to design a joint that more evenly distributes the forces occurring at the connection between components. For example, it is generally known to utilize a T-joint for connecting a root end of a wind turbine blade which is made from a composite material to a metallic rotor hub. In this design, a plurality of axial bores is formed along the circumference in the root end of the blade. Additionally, a plurality of radial bores, such as blind bores or through bores, is formed in the side wall of the root end of blade so as to intersect a corresponding axial bore. A metal insert having a threaded bore is then positioned in each of the radial bores in the side wall of the blade. Stud bolts are then inserted into the axial bores and threadably engaged with the threaded bores of the metal inserts to form the T- joint and thereby retain the stud bolts at the root end of the blade. The stud bolts are secured to the rotor hub.

[0008] While current connection joints are sufficient to achieve their intended purpose of supporting the loads, one drawback is that as the size of wind turbine blades continues to increase, the strength of the connection joint will also have to increase. One potential solution is to simply increase the size of the components. The increase in strength is provided by an increase in the amount of material present. This approach, however, requires additional material and increases manufacturing costs. There may also be some practical size limitations that render this approach undesirable.

[0009] Another solution may be to simply increase the number of connecting bolts between the two components. In other words, the connecting bolt density (i.e., the number of bolts per length of circumference) may be increased. This approach, however, also has limitations. In this regard, the formation of axial bores and radial bores (e.g., for T-joints) removes material from the composite. As the connecting bolt density increases, the amount of void space in the component increases. Should too much material be removed, the structural integrity of the composite component may become compromised. Thus, as a practical matter there may be a limit to the number of connecting bolts that can be used for a given dimension of the composite component. As a result, the connecting interface has to be larger, which suffers from the cost issues identified above.

[0010] For the reasons outlined above, manufacturers continually strive to provide a connection joint for connecting metallic components to composite components and for connecting two composite components that accommodates increased loading of the blades in a cost-effective manner and without sacrificing the structural integrity of the composite component. In other words, it is desirable to have a high strength connection (e.g., high load capability) with a relatively small connection interface size. Summary

[0011] To these and other ends, a hub segment for use on a wind turbine includes a funnel-like body having a flared end and a stem. The flared end is configured to be coupled to a hub of a wind turbine and includes a rim and a side wall extending away from the rim and a plurality of connecting elements integrated into the flared end and spaced apart from the rim. Each connecting element includes an eye that defines a bore through the side wall of the flared end. The stem is configured to fit within a root end of a wind turbine blade.

[0012] Each of the plurality of connecting elements includes a folded roving of fibers, wherein the eye of the plurality of connecting elements is defined at least in part by the fold in the fiber rovings. The folded roving of fibers defines a through hole, each connecting element further including an insert positioned in the through hole such that a portion of the through hole and a portion of the insert forms a boundary of the eye in each of the connecting elements. The roving of fibers includes stacked plies of fiber material and includes unidirectional fiber plies. The fibers include glass fibers, carbon fibers, or combinations thereof. At least a portion of the eyes of the plurality of connecting elements is formed by longitudinal side walls of the fiber rovings such that there are substantially no fiber endings at a boundary of the eyes along the portion formed by the fiber rovings. Each of the plurality of

connecting elements is made entirely from a composite material and are wedge shaped. The flared end is a molded article and the plurality of connecting elements is integrated into the flared end during molding.

[0013] The hub segment further includes a plurality of cross pins configured to be inserted through respective eyes of the plurality of connecting elements. When the cross pins are received in the eyes, an exposed portion of the cross pins is configured to extend away from at least one surface of the side wall of the flared end of the hub segment. In one embodiment, when the cross pins are received in the eyes, an exposed portion of the cross pins is configured to extend away from an outer surface of the side wall and an inner surface of the side wall of the flared end. The cross pins include one or more grooves configured to receive a fastener. The cross pins may also include a pair of opposed bosses to provide a T-shaped cross pin, wherein each of the bosses includes a through hole configured to receive a fastener. The cross pins are slidably insertable into respective eyes of the plurality of connecting elements and are not otherwise fixedly secured to the flared end of the hub segment.

[0014] The hub segment further comprises a plurality of fasteners for securing the flared end to the hub. The fasteners are configured to engage with an exposed portion of the cross pins when the cross pins are received through respective eyes of the plurality of connecting elements. The plurality of fasteners includes a plurality of U-bolts. A hub assembly for use with a hub on a wind turbine comprises at least two hub segments coupled together. The hub assembly further comprises a plurality of cross pins inserted through respective eyes of the plurality of connecting elements on each of the at least two hub segments. When the cross pins are received in the eyes, an exposed portion of the cross pins extends away from at least one surface of the side wall of the flared end of each of the at least two hub segments.

[0015] A hub segment for use with a wind turbine blade includes a funnel-like body having a flared end and a stem having a tip. The flared end is configured to be coupled to a hub of a wind turbine and the stem is configured to fit within a root end of the wind turbine blade to define a region of overlap between the root end and the stem. A pitching mechanism includes at least two bearings in the region of overlap for rotatably coupling the wind turbine blade to the hub segment. An elastomeric bushing between at least one of the at least two bearings and the wind turbine blade. The two bearings are spaced apart within the region of overlap with one bearing at the tip of the stem. One of the bearings is a ball bearing. A reinforcement member includes a cap plate and a tie rod secured to the cap plate at one end.

[0016] A method of making a hub segment having a flared end includes providing a molding apparatus having a molding surface and a plurality of connecting elements, each connecting element includes a folded roving of fibers which defines an eye; laying a first assembly of fiber plies in the molding apparatus and inserting the plurality of connecting elements in the molding apparatus; laying a second assembly of fiber plies in the molding apparatus, wherein the plurality of connecting elements are generally positioned between the first and second assembly of fiber plies; Infusing resin into the first and second assemblies of fiber plies; and curing the fiber plies and resin to form the flared end of the hub segment, the flared end having a face portion and a side wall extending therefrom. The plurality of connecting elements is arranged in the molding apparatus such that at least a portion of each eye defines a bore through the side wall of the flared end which is spaced from the face portion.

[0017] The method further comprises providing a plurality of anchors in the molding apparatus, the anchors coupled to the molding surface and extending therefrom, and supporting each of the connecting elements on one anchor of the plurality of anchors such that each anchor extends through the eye in one of the connecting elements. The anchors are removably coupled to the molding apparatus. The method further includes removing the anchors from the molding apparatus and de-molding the flared end of the hub segment from the molding apparatus.

[0018] In another embodiment, a wind turbine comprises a tower, a nacelle positioned atop of the tower, a rotor coupled to the nacelle that includes a hub assembly having a hub and at least one hub segment having a flared end with a rim and a side wall extending away from the rim. The flared end of the hub segment is coupled to the hub by a connection joint, wherein the

connection joint comprises a plurality of connecting elements integrated into the flared end of the hub segment. Each connecting element includes an eye that defines a bore through the side wall of the flared end and which is spaced from the rim. A plurality of cross pins may be received through respective eyes of the plurality of connecting elements which form the bores in the side wall of the flared end, wherein the cross pins include an exposed portion that extends away from at least one surface of the side wall. A plurality of fasteners engages the exposed portion of the cross pins and couple to the hub for securing the hub segment to the hub. The exposed portion of the cross pins extends away from an outer surface and an inner surface of the side wall and a fastener engages the exposed portion extending from both the inner and outer surfaces of the side wall.

[0019] In yet another embodiment, a wind turbine comprises a tower, a nacelle positioned atop of the tower, a rotor coupled to the nacelle that includes a hub assembly with a hub and at least one hub segment coupled to the hub and including a flared end and a stem. At least one wind turbine blade includes a root end received over the stem to form a region of overlap between the stem and the root end. A pitching mechanism includes at least two bearings in the region of overlap for rotatably coupling the wind turbine blade to the at least one hub segment. An elastomeric bushing is positioned between at least one of the at least two bearings and the wind turbine blade. The stem of the hub segment has a tip and the at least two bearings are spaced apart within the region of overlap with one bearing at the tip. At least one of the bearings is a ball bearing. The stem of the hub segment includes a tip and the wind turbine further comprises a reinforcement member including a cap plate at the tip of the stem, a tie rod, and a post secured to the hub, the tie rod being secured to the cap plate at one end and secured to the post at an opposite end.

Brief Description of the Drawings

[0020] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate one or more embodiments of the invention and, together with a general description of the invention given above, and the detailed description given below, serve to explain the invention.

[0021] Fig. 1 is a perspective view of a wind turbine in which

embodiments of the invention may be used;

[0022] Fig. 2 is a partial perspective view of a hub assembly with wind turbine blades according to one embodiment of the invention;

[0023] Fig. 2A is a perspective view of the hub assembly shown in Fig. 2;

[0024] Fig. 3 is a perspective view of a hub segment in the hub assembly shown in Fig. 2;

[0025] Fig. 4 is a perspective view of a hub according to one embodiment of the invention;

[0026] Fig. 5 is a cross sectional view of the hub segment shown in Fig. 3 taken generally along the line 5-5;

[0027] Fig. 6 is a perspective view of a connecting element according to one embodiment of the invention;

[0028] Fig. 7 is top plan view of the connecting element shown in Fig. 6;

[0029] Fig. 8 is a side view of the connecting element shown in Fig. 6;

[0030] Figs. 9A-9D schematically illustrate a method for making the connecting element shown in Figs. 6-8;

[0031] Figs. 10A and 10B schematically illustrate a molding apparatus for making a hub segment having the connecting elements integrated therein;

[0032] Figs. 1 1 A and 1 1 B schematically illustrate a molding method for making the hub segment having the connecting elements integrated therein; [0033] Fig. 12 is an exterior view of a connection joint in accordance with one embodiment of the invention;

[0034] Fig. 13 is a cross-sectional view of the connection joint shown in Fig. 12;

[0035] Fig. 14 illustrates a cross pin for the connection joint shown in Figs. 12 and 13;

[0036] Fig. 15 is a perspective view of a fastener according to one embodiment of the invention;

[0037] Fig. 16 is a cross-sectional view of a selected portion of the hub assembly shown in Fig. 2; and

[0038] Fig. 16A is an enlarged view of the bearing shown in Fig. 16. Detailed Description

[0039] With reference to Fig. 1 , a wind turbine 10 includes a tower 12, a nacelle 14 disposed at the apex of the tower 12, and a rotor 16 operatively coupled to a generator (not shown) housed inside the nacelle 14. In addition to the generator, the nacelle 14 houses miscellaneous components required for converting wind energy into electrical energy and various components needed to operate, control, and optimize the performance of the wind turbine 10. The tower 12 supports the load presented by the nacelle 14, the rotor 16, and other components of the wind turbine 10 that are housed inside the nacelle 14 and also operates to elevate the nacelle 14 and rotor 16 to a height above ground level or sea level, as may be the case, at which faster moving air currents of lower turbulence are typically found.

[0040] With reference to Figs. 1 and 2, the rotor 16 of the wind turbine 10, which is represented as a horizontal-axis wind turbine, serves as the prime mover for the electromechanical system. Wind exceeding a minimum level will activate the rotor 16 and cause rotation in a plane substantially perpendicular to the wind direction. According to embodiments of the present invention, rotor 16 of wind turbine 10 includes a multi-component hub assembly 18 (described below), at least one wind turbine blade 20 that projects outwardly from the hub assembly 18 at locations circumferentially distributed thereabout. In the representative embodiment, the hub assembly 18 carries three wind turbine blades 20, but the number of wind turbine blades may vary. The wind turbine blades 20 are configured to interact with the passing air flow to produce lift that causes the hub assembly 18 to spin about a central longitudinal axis.

[0041] The wind turbine 10 may be included among a collection of similar wind turbines belonging to a wind farm or wind park that serves as a power generating plant connected by transmission lines with a power grid, such as a three-phase alternating current (AC) power grid. The power grid generally consists of a network of power stations, transmission circuits, and substations coupled by a network of transmission lines that transmit the power to loads in the form of end users and other customers of electrical utilities. Under normal circumstances, the electrical power is supplied from the generator to the power grid as known to a person having ordinary skill in the art.

[0042] With reference to Figs. 2 and 2A, the wind turbine blades 20 are coupled to the hub assembly 18 in a manner that allows the wind turbine blades 20 to rotate or pitch about a longitudinal axis of the wind turbine blades 20. This may be achieved by coupling a root end or a region of the wind turbine blade 20 near the root end to one or more bearing assemblies operatively coupled to the hub assembly 18. This aspect of the invention is described below in conjunction with Figs. 2 and 16. The hub assembly 18 may include multiple individual components that are coupled together. In the exemplary embodiment shown, the hub assembly 18 includes one or more hub segments 22 coupled to a hub 24. A rotor shaft 26 may extend from and be coupled to the hub 24. A wind turbine blade 20 extends from and may be operatively coupled to each hub segment 22. Rotation of the hub assembly 18 rotates the rotor shaft 26. This in turn causes the generator (not shown) to generate electrical energy so that electrical energy may be distributed from the wind turbine 10 to a power grid.

[0043] As shown in Fig. 2A, the exemplary hub assembly 18 includes three hub segments 22. Each hub segment 22 is coupled to the hub 24 and to the other two hub segments 22. The hub segments 22 may be coupled to the hub 24 prior to hoisting the hub assembly 18 into position at the apex of the tower 12. Alternatively, each of these individual components may be hoisted into position on the tower 12 prior to their connection. Advantageously, each of the components may be separately manufactured and then individually shipped to the installation site prior to assembly. In this way, larger, stronger hubs may be manufactured while avoiding transportation and manufacturing issues. As will be described below, the hub assembly 18 according to embodiments of the invention may be also lighter in weight in comparison to cast hubs of

comparable strength. This may improve the efficiency of the wind turbine 10 relative to comparably sized wind turbines.

[0044] With reference to Figs. 2, 2A, and 3, the hub segment 22 may appear as a funnel-like body with a mouth or flared end 30 at which the hub segment 22 is coupled to the hub 24 and to adjacent hub segments 22. A finger-like extension or stem 32 of the hub segment 22 terminates at a tip 28 generally opposite the flared end 30. The stem 32 may have a cylindrical configuration over which a root end 34 of the wind turbine blade 20 is received. Alternatively, the stem 32 may be conical or tapered along its length. The arrangement of the wind turbine blade 20 on the stem 32 is shown in Fig. 2 and is described below in conjunction with Fig. 16.

[0045] With reference to Fig. 3, the flared end 30 has a rim 36 that forms one portion of a connection joint described below in the hub assembly 18. In that regard, the hub segment 22 is coupled to the hub 24 and adjacent hub segments 22 at the rim 36 (see Fig. 2). The rim 36 may have a non-planar configuration divided into four face portions 38a, 38b, 40a, and 40b. The face portions 38a and 38b follow an arcuate portion of the flared end 30 and define individual, separate planes that mate to corresponding face portions on adjacent hub segments 22, as can be appreciated by Fig. 2. The face portions 40a and 40b may collectively define a plane, but embodiments of the invention are not limited to that configuration. The face portions 40a and 40b may also correspond and mate to face portions on the hub 24 shown in Fig. 4, described below.

[0046] In accordance with an aspect of the invention, and as illustrated in Fig. 3, a plurality of connecting elements 42 are integrated into the hub segment 22 proximate the rim 36. The connecting elements 42 may be circumferentially spaced about the rim 36 in a sidewall of the hub segment 22 and may be embedded within the material that forms the sidewall. A method for integrating the connecting elements 42 within the sidewall of the hub segment 22 will be described more fully below. The number of connecting elements 42 along the circumference of the flared end 30 of the hub segment 22 depends on the size of the hub assembly 18 and the number of hub segments 22, among potential other factors, but may be anywhere from 100 to 250 connecting elements 42 for use with wind turbine blades 20 of between 50m and 80m in length. More or fewer connecting elements 42 may be used depending on the specific application. As will be explained more fully below, one aspect of the present invention is to allow a close packing of connecting elements 42 without negatively impacting the structural integrity of the hub assembly 18. The connecting elements 42 include a passage or eye 44 through which a fastener may pass so as to join the hub segment 22 to the hub 24 and to adjacent hub segments 22. Each of these joints is described below.

[0047] In that regard, and as is shown in Figs. 2 and 4, the hub 24 may include flanges 46 and 48 spaced apart by a support member 52. In the embodiment shown, the support member 52 is a hollow conical shell to which the rotor shaft 26 may be secured or which forms a part of the rotor shaft. Each of the flanges 46 and 48 may be secured to the support member 52, for example, by welds though embodiments of the invention are not limited to a welded construction. The support member 52, the flanges 46 and 48, and the rotor shaft 26 may form a welded hub structure. Advantageously, this welded structure may be significantly lighter in weight than comparable monolithic, casted hubs and so may be easier to manufacture, transport, and install though the welded structure in combination with the hub segments 22 may be characterized as having a significant improvement in strength relative to conventional monolithic, cast hubs.

[0048] With reference to Fig. 4, in one embodiment, each of the flanges 46 and 48 is triangular in shape and defines three sides (i.e., three sides labeled 54a and three sides labeled 54b, respectively). As shown, each flange 46 and 48 may not be a perfect triangle as each of the three sides 54a and 54b may not intersect but are truncated at each end by relief sides 60a and 60b, respectively. Relief sides 60a and 60b may elevate any mismatch in geometry with the hub segments 22 during assembly by provide a relief region 62 (see Fig. 2A). The sides 54a and 54b are arranged to form connection joints with the face portions 40a and 40b of the rim 36. That is, collectively, pairs of sides 54a and 54b may mate to face portions 40a and 40b, respectively, as is generally shown in Figs. 2 and 2A.

[0049] To that end, each flange 46 and 48 includes a plurality of bores 56 spaced along each of the sides 54a and 54b. As shown in Figs. 2 and 2A, the bores 56 may correspond in number and in spacing to the eyes 44 in each the flared end 30 of the hub segment 22 and receive a fastener. During assembly of each of the hub segments 22 to the hub 24, the face portions 40a and 40b may abut the sides 54a and 54b, respectively, and so collectively form a joint interface between the hub 24 and the hub segment 22 as is shown in Fig. 2.

[0050] In accordance with an aspect of the invention, and as illustrated in Figs. 5-8, the connecting elements 42 may be formed from a composite material comprising fibers, such as glass or carbon fibers, and a suitable resin material, such as epoxy. This is in contrast to conventional connecting elements, such as those described above, which are typically formed from metals, such as steel. In a preferred embodiment, the connecting elements may be mostly formed, if not entirely formed, by non-metallic materials. By way of example, the connecting elements 42 may be entirely formed from a composite material. Alternatively, the majority of the connecting element (e.g., greater than 50%, and preferably greater than 80%) may be formed from a composite material. Forming the connecting elements 42 entirely or mostly from a composite material not only reduces the weight of each of the hub segments 22, but also reduces the costs associated with the connecting elements since the composite connecting elements 42 may be formed from relatively cheap materials and in a cost effective manner, as will be explained in detail below. Furthermore, forming the connecting elements 42 from composite materials may allow the connecting elements 42 to be integrated into the material of the hub segment 22 (which is also formed from a composite material) in a manner that provides an increase in the strength of the joints between adjacent hub segments 22 and between each of the hub segments 22 and the hub 24.

[0051] In an exemplary embodiment, a connecting element 42 may be configured as an elongated wedge-shaped member 70 having a head end 72, a tip end 74, a top surface 76, a bottom surface 80, a first side surface 82, a second side surface 84, a head end surface 86, and a tip end surface 90. The top and bottom surfaces 76, 80 may be generally planar or consist of generally planar portions, and converge toward each other in a direction toward the tip end 74 of the connecting element 42 along at least a portion of the length of the connecting element 42. By way of example and without limitation, the top and bottom surfaces 76, 80 may converge toward each other for the entire length of the connecting element 42. Alternatively, the top and bottom surfaces 76, 80 may be generally parallel to each other for a short distance from the head end 72, for example for about 5%-10% of the total length of the connecting element 42, and then converge toward each other along the remaining length of the connecting element 42. In an exemplary embodiment, the taper angle Ai of the top and bottom surfaces 76, 80 may be between about 2 and 30 degrees, preferably between about 4 and 25 degrees, still preferably between about 5 degrees and about 15 degrees. Other values for the taper angle A-i may also be possible. The wedged configuration of the connecting element 42 facilitates the integration of the connecting element 42 into the material of the hub segment 22 and increases the bond strength between the connecting element 42 and the material in which it is integrated.

[0052] In addition to the above, the first and second sides 82, 84 of the connecting element 42 may also be tapered in a direction toward the tip end 74 of the connecting element 42. By way of example and without limitation, the first and second side surfaces 82, 84 may converge toward each other for the entire length of the connecting element 42. Alternatively, the first and second side surfaces 82, 84 may be generally parallel to each other for a short distance from the head end 72, for example for about 5%-10% of the total length of the connecting element 42, and then converge toward each other along the remaining length of the connecting element 42. In an exemplary embodiment, the taper angle A ₂ of the first and second side surfaces 82, 84 may be between about 2 degrees and about 10 degrees. Other values for the taper angle A ₂ may also be possible. The tapering in the sides 82, 84 of the connecting element 42 provides an increased contact area between the connecting element 42 and the material of the hub segment 22 in a region between adjacent, circumferentially spaced connecting elements 42. Again, this increases the bond strength between the connecting element 42 and the surrounding material.

[0053] As further illustrated in the figures, the head end surface 86 may have a curved or arcuate configuration and smoothly transition to the first and second side surfaces 82, 84. By way of example and without limitation, the head end surface 86 may be generally circular with a radius of curvature R-i between about 1 cm and about 6cm, preferably between about 1 .5cm and 4cm. Furthermore, the connecting element 42 may include a through hole 92 adjacent the head end 72 of the connecting element 42. The through hole 92 extends from the top surface 76 to the bottom surface 80. For reasons that are more fully described below, the through hole 92 has an arcuate (e.g., semicircular) first end 94 and a generally v-shaped second end 96. An insert 100 may be positioned in the through hole 92 so as to substantially fill a portion of the through hole 92 adjacent the v-shaped second end 96. The insert 100 is configured to only fill a portion of the through hole 92, and thereby define the passage or eye 44 adjacent the first end 94 of the through hole 92 which extends from the top surface 76 to the bottom surface 80. In one embodiment, the insert 100 may be generally triangularly shaped and be formed from a composite material. The composite material of the insert 100 may be the same or different than the composite material of the remaining portions of the connecting element 42. By way of example, the insert 100 may be formed from a glass or carbon fiber and a resin material, such as a suitable epoxy resin. However, other materials may also be used to form the insert 100. In embodiments, the insert may be formed from wood such as balsa wood or balsa wood impregnated for additional stiffness. In still further aspects, the insert 54 may be made from a resin material or other plastics material.

Preferably, the material od the insert 54 may have a thermal expansion coefficient similar to the thermal expansion coefficient of the resin-embedded rovings. These materials should be compatible with the composite material of the member 70 so as to provide a strong bond therebetween. A top surface of the insert 100 may be selected such that the eye 44 has a desired shape. For example, the top surface may be flat or may be curved.

[0054] In the disclosed embodiment, the eye 44 in the connecting element 42 may be bounded in part by the insert 100 and in part by the wedge- shaped member 70 that forms at least a portion of the connecting element 42. In one aspect of the invention, the through hole 92 and the eye 44 through the connecting element 42 is not formed by a drilling or machining operation that tends to cut or otherwise break the fibers of the member 70, thereby creating fiber ends at the boundary of the drilled or machined bores. The through holes 92 of the connecting elements 42 may be formed without a post drilling or milling operation, and without cutting or breaking the fibers that form the connecting elements 42. It is believed that providing the through hole 92 and the eye 44 that is not the result of a drilling or milling process, such that the boundary of the through hole 92 or eye 44 is not formed by cut ends of the fiber material, will increase the strength of the flared end 30 in the area of the eye 44. This is particularly relevant because the forces on the hub segment 22 are transferred to the hub 24 and to adjacent hub segments 22 through this region.

[0055] Figs. 9A-9D schematically illustrate an exemplary process for forming the connecting elements 42 having the eye 44 as described above. In this regard, an elongate mandrel 102 may be provided having a U-shaped or D- shaped cross sectional profile. Such a profile provides a pair of opposed, generally planar side surfaces 104, 106 and an arcuate or curved top surface 1 10. The shape of the top surface 1 10 may be selected so as to correspond with the shape of the first end 94 of the through hole 92. Thus, in one

embodiment, the curved top surface 1 10 may be semicircular with a radius of curvature between about 0.4cm and about 2cm, preferably between about 0.4cm and about 2cm; preferably between about 0.5cm and 1.5cm. This range should be between 10% and 50% below the radius of curvature of the head end surface 86. A bottom side 1 12 of the mandrel 102 may be closed off by a surface or be open. The mandrel 102 may be formed of metal or other suitable material known to those of ordinary skill in the art.

[0056] The insert 100 that is eventually coupled to the through hole 92 to form the eye 44, which may be provided as an elongate member having the desired cross-sectional configuration (e.g., triangular), may be temporarily secured to the bottom side 1 12 of the mandrel 102 so as to depend therefrom. At this point, a plurality of finite length fiber rovings may be essentially folded over the top surface 1 10 of the mandrel 102 such that the fiber rovings drape down from the side surfaces 104, 106 of the mandrel 102. The center region of the fiber rovings are adjacent the top surface 1 10 of the mandrel 102 and the ends of the fiber rovings are then brought together at the tip end 74.

Accordingly, the fiber rovings generally conform to the shape of the top surface 1 10 and side surfaces 104 and 106 of the mandrel 102 and to the side surfaces of the insert 100 depending from the bottom side 1 12 of the mandrel 102.

[0057] Bringing the ends of the fiber rovings together provides a tapering configuration that provides the taper in the first and second side surfaces 82, 84 in the connecting element 42. The fiber rovings may be provided by stacking a plurality of fiber sheets or plies 1 14. The fiber plies 1 14 may be dry fiber plies or resin-impregnated fiber plies (e.g., pre-preg) either uncured, partially cured or combinations thereof. The fiber plies 1 14 may further be unidirectional fiber plies, biaxial fiber plies, or a combination thereof in a wide range of ordered configurations (e.g. , a repeated pattern of three unidirectional plies and one biaxial plies). The number of fiber plies 1 14 that are stacked onto the mandrel 102 may be selected so as to provide the desired width in the connecting element 42. Additionally, the length of the fiber plies 1 14 may be selected so as to provide the desired length in the connecting element 42. The width of the fiber plies and 14 may be selected so as to fit on the length of the mandrel 102. As explained below, ultimately, a composite article 120 formed from this process is subject to further processing so as to provide a plurality of

connecting elements 42.

[0058] Once the layup process of the fiber plies 1 14 on the mandrel 102 is complete, and with reference to Figs. 9B and 9C, the article 120 may be fully cured or at least partially cured by a suitable curing process known to those of ordinary skill in the art. Subsequent to the curing process, the article 120 may be removed from the mandrel 102 such that the article 120 includes the fiber plies 1 14, resin, and the insert 100 integrated together, as is shown best in Fig. 9C. From here, the article 120 may be subject to post processing techniques to form a plurality of connecting elements 42 from the article 120. In this regard, the article 120 may be subject to a cutting operation (e.g., from a wire cutter 122) so as to form discrete connecting elements 42 (shown in Fig. 9D). As can be appreciated, the cutting operation on the article 120 forms the top and bottom surfaces 76, 80 of the connecting element 42. The cutting operation is configured so as to form the tapered configuration in the thickness direction of the connecting elements 42.

[0059] The process described above results in each of the connecting elements 42 having the shape and geometry described above. The process is particularly beneficial for producing a through hole in the connecting element without cutting the fibers that form the composite member. In particular, the head end 72 of the connecting elements 42 may be formed by the longitudinal side surfaces of continuous strands of fibers. There are essentially no fiber ends at the boundary of the through hole 92. The connecting element 42 with through hole 92 may be thought of as a folded roving of fibers that, through the folding of the fibers creates, an eye through the element 42. For this reason, the connecting elements 42 may be referred to as roving eyes. In any event, the arrangement of the fibers in the roving eye which create the through hole 92 as part of the fiber arrangement is believed to significantly increase the strength of the flared end 30 of the hub segments 22. The connecting elements 42 may vary in size as required by the application. In an exemplary embodiment, a connecting element 42 may have a length between about 15cm and about 1 .5m; preferably between about 25cm and about 1 m; a width (at the head end) between about 20cm and about 6cm; and a height (at the head end) between about 4cm and about 20cm. These ranges are merely exemplary and the invention is not limited to these values.

[0060] With the individual connecting elements 42 now formed through, for example, the process described above, the integration of the connecting elements 42 into the flared end 30 of the hub segment 22 will now be described in more detail. In this regard, Figs. 10A-1 1 B schematically illustrate an exemplary method of integrating the connecting elements 42 into the hub segment 22. In one embodiment, the hub segment 22 may be formed through a molding process using a molding apparatus 130 defining an inner surface 132 for defining the hub segment 22. A plurality of pegs or anchors 134 may be removably secured to the inner surface 132 of the molding apparatus 130 adjacent a first end of the molding apparatus 130. The number and position of anchors 134 may correspond to the number and position of connecting elements 42 desired in the hub segment 22. The anchors may be formed from a suitable thermoplastic polymer that facilitates removal of the hub segment 22 from the molding apparatus 130 after curing (e.g., having desired thermal expansion properties). By way of example and without limitation, the anchors 134 may be formed from polytetrafluoroethylene (PTFE). Other materials, however, may also be acceptable.

[0061] The molding method may include placing a release agent 136 such as a liquid release coating, a wax, or a solid barrier (e.g., Teflon® tape) over the inner surface 132 of the molding apparatus 130. An optional layer (not shown) of release material (e.g., film) may then be applied over the release agent 136. In addition, a first optional layer of peel ply 140 may be applied over the release material layer, if present, or directly over the release agent 136. Next, several layers 142 of the fiber fabric may be placed over one another (e.g., stacked) to define an assembly of layers 144, until a desired,

predetermined thickness is reached in accordance with the design. The fiber fabric may include glass fiber, carbon fiber or other material or combination of materials known to those of ordinary skill in the art. The fiber fabric may be resin-impregnated (e.g., a pre-preg) or be dry. The layers 142 of the first assembly of layers 144 may be laid up in the molding apparatus 130 so as to define a taper 146 in the stack.

[0062] After the first assembly of layers 144 has been laid in the molding apparatus 130, the connecting elements 42 may be located in the mold. In this regard, the anchors 134 may have a shape that corresponds to the shape of the eye 44 in the connecting elements 42 such that the connecting elements 42 may be hung or supported from the anchors 134. The taper of the bottom surface 80 of the connecting elements 42 generally correspond to the taper 146 of the first assembly of fiber layers 144. After locating the connecting elements 42 in the molding apparatus 130, additional layers 150 of the fiber fabric may be placed over one another to define a second assembly of layers 152, until a desired, predetermined thickness is reached in accordance with the design. Similar to above, the fiber fabric may include glass fiber, carbon fiber or other material or combination of materials known to those of ordinary skill in the art. The fiber fabric may be resin-impregnated or be dry. The layers 150 of the second assembly of layers 152 may be laid up in the molding apparatus 130 so as to define a taper 154 in the material. The taper 154 in the material may generally correspond to the taper in the top surface 76 of the connecting element 42.

[0063] In accordance with an aspect of the invention, the rim 36 of the hub segment 22 may include a composite rim support 156 above the head ends 72 of the connecting elements 42. In this regard, the space between the head ends 72 of adjacent connecting elements 42 (resulting from the arcuate shape of the head ends) may be filled with a dry or resin-impregnated fiber material. By way of example, if the connecting elements 42 are next to each other, a wedge-shaped fiber insert (not shown) may be positioned in the space such that there are essentially no gaps in fibrous material in the region of the head ends 72 of the connecting elements 42. Additional fiber layers may be added above the head ends 72, such as that provided by a fiber tape or bandage. It is the outermost layer of the fiber tape that will result in the face portions 38a, 38b, 40a, and 40b at the flared end 30 of the hub segment 22. Thus, between the first assembly of layers 144 and the second assembly of layers 152, and the fiber inserts, the connecting elements 42 are essentially embedded within the composite material of the flared end 30 of the hub segment 22.

[0064] Once this assembly is reached, a second optional peel ply 160 made, for example, of nylon or some other tightly woven fabric impregnated with a release agent, may be applied over the formed assembly. Once the second optional peel ply 160 is in place, a layer 162 of release film may be applied thereover. In this embodiment, a breather or bleeder material layer 164 may then be applied over the second optional peel ply 160, which is configured to absorb excess resin and let gases escape during formation of the composite laminate.

[0065] With continued reference to Figs. 1 1 A and 1 1 B, a vacuum bag 166 may be placed over the above-mentioned layers and secured in place against the molding apparatus 130 via a securing element 170, such as a bag sealant tape, and a vacuum source 172 actuated. Actuation of the vacuum source 172 is effective to pull the bag 166 toward the inner surface 132 of the molding apparatus 130 so as to give shape to the flared end 30 of the hub segment 22. The vacuum source 172 is also effective to remove air as well as excess resin from the assembly of fiber layers and resin. When the fiber layers are not pre-impregnated with resin, but are instead dry layers of fiber, a resin distribution system (not shown) may be placed in communication with the layers under the vacuum bag 166 and used to distribute resin to the fiber layers.

These steps are generally known in the art and will not be described in further detail.

[0066] In a subsequent step, the resulting assembly is allowed to cure or at least partially cure within the molding apparatus 130, such as through a heating process. Once cured or at least partially cured, the anchors 134 may be removed from molding apparatus 130 and the hub segment 22 removed from the molding apparatus 130. As noted above, the hub segment 22 now includes radial openings or bores provided by the eyes 44 of the connecting elements 42. Again, these bores were not formed from a drilling or machining process, but in the formation of the flared end 30 of the hub segment 22 itself, and more particularly in the formation of the connecting elements 42 which are integrated into the flared end 30 of the hub segment 22.

[0067] With an improved design of the flared end 30 of the hub segment 22 described above, an exemplary embodiment will now be described directed to coupling of the hub segment 22 to the hub 24 and to coupling of the hub segment 22 to an adjacent hub segment 22. Each of these connections is shown in Fig. 2. In this regard and in further reference to the figures, the flared end 30 of the hub segment 22 may be coupled to two hub segments 22 and to the hub 24. The hub segments 22 may form a continuous ring-like structure within which the hub 24 is positioned.

[0068] The connect joint between hub segments 22 and between the hub segment 22 and the hub 24 is not limited to any particular configuration of fastener. In one exemplary embodiment illustrated in Figs. 12-15, a connection joint 200 between the hub segment 22 and the hub 24 (and/or between adjacent hub segments 22) includes a plurality of T-shaped slide members or cross pins 202 configured to be engaged with the eyes 44 of the connecting elements 42 and a plurality of fasteners 204 for coupling opposing cross pins 202 together.

[0069] The cross pins 202 have a cross-sectional shape that generally matches the shape of the eyes 44 of the connecting elements 42. In this embodiment, the cross pins 202 include an elongate body 210 having generally planar top and bottom surfaces 212, 214; first and second generally planar side surfaces 216, 218; a generally arcuate first end surface 220; and a second end surface 222. The size of the cross pin 202 is such as to fit within the eyes 44 of the connecting elements 42. The first end surface 220 may be curved to generally correspond to the curvature of the head end of the eye 44. The second end surface 222 may be generally planar and correspond to a generally planar surface of the insert 100. Alternatively, however, the second end surface 222 may also be generally arcuate having, for example, a radius of curvature substantially equal to the radius of curvature of the first end surface 220. The first and second side surfaces 216, 218 include generally rectangular bosses 224, 226 extending therefrom and adjacent the top surface 212 (e.g., so as to be flush or planar therewith) so that the cross pin 202 is generally T-shaped. Each of the bosses 224, 226 include a through bore 230 extending between first and second end surfaces of the bosses. Additionally, the second end surface 222 may further include a groove 232 adjacent the bottom surface 214 that extends across the end surface 222 in a direction generally transverse to a longitudinal direction of the cross pin 202. The groove 232 may be generally arcuate in cross section. In an exemplary embodiment, the cross pins 202 may be formed from metal, such as steel. However, other suitable materials may also be possible.

[0070] As described above and shown in Figs. 2, 2A, and 4, the hub 24 may include bores 56 spaced apart and positioned along each side 54a, 54b of corresponding flanges 46, 48. In this way, the bores 56 of the hub 24 may receive cross pins 202 similar to those received in the eyes 44 of the

connecting elements 42 in the flared end 30 of the hub segment 22. To facilitate a coupling between the hub segment 22 and the hub 24, cross pins 202 may be inserted through the eyes 44 of the connecting elements 42, either from exterior to interior or interior to exterior of the hub segment 22. The bosses 224, 226 extend outboard of the eyes 44 such that that portion of the cross pin 202 (e.g., the cross portion of the T) cannot pass through the eyes 44 and therefore engage an exterior or interior side wall surface of the hub segment 22. In an exemplary embodiment, adjacent cross pins 202 in a circumferential direction of the flared end 30 alternate in the orientation of the cross pins 202. Thus, the bosses 224, 226 of a cross pin 202 may engage the exterior surface of the flared end 30 while the bosses of an adjacent cross pin 202 engage the interior surface of the flared end 30, and vice versa. This alternating pattern is repeated along the perimeter of the flared end 30 of the hub segment 22.

[0071] In a similar manner, cross pins 202 may be inserted through the bores 56 in the hub 24, either from a first side of each flange 46, 48 to a second side of each flange 46, 48, or from a second side to a first side of each flange 46, 48. The bosses 224, 226 extend outboard of the bores 56 such that that portion of the cross pins 202 cannot pass through the bore 56 and therefore engage a first or second surface of the hub 24. In an exemplary embodiment, adjacent cross pins 202 in a circumferential direction of the hub 24 alternate in the orientation of the cross pin 202. Thus, the bosses 224, 226 of a cross pin 202 may engage the first side surface of the flanges 46, 48 while the bosses of an adjacent cross pin 202 engage the second side surface of the flanges 46, 48, and vice versa. This alternating pattern is repeated along each of the sides 54a, 54b of the flanges 46, 48 of the hub 24. However, the alternating pattern in the flared end 30 of the hub segment 22 and the alternating pattern in the hub 24 are opposite to each other such that axially aligned cross pins 202 across the connection joint 200 have opposite orientations. [0072] In this embodiment, the fasteners 204 include U-bolts 206 having a central portion 240 and opposed legs 242 with threaded ends 244 to secure the flared end 30 of the hub segment 22 to the hub 24. In this regard, and with regard to a pair of axially aligned cross pins 202 and on a first side (e.g., or the exterior of first end and hub member), the threaded ends 244 of a U-bolt 206 may be inserted through the bores 230 in the bosses 224, 226 of one of the cross pins 202 and the central portion 240 of the U-bolt 206 may be seated within the groove 232 in the other cross pin 202 axially aligned across the joint interface. Suitable nuts 250 may be threadably engaged with the threaded ends 244 of the U-shaped bolts 206 to secure the flared end 30 of the hub segment 22 to the hub 24. The same process may be used between the flange 48 and the hub segment 22. Notably, however, the orientation of the U-bolt 206 on the second side is opposite to that on the first side of the connection joint. In other words, if a cross pin includes the threaded ends 244 and nuts 250 of a U- bolt 206 on a first side of a connection joint 200 (e.g., exterior side of flared end 30 or first side of flange 46), then the same cross pin includes the central portion 240 of a U-bolt 206 on the other side of the connection joint 200 (e.g., interior side of flared end 30 or second side of flange 46). Thus, for an aligned pair of cross pins 202 there is a symmetry that more evenly balances the forces. It is believed that the connection joint 200 not only provides a stronger joint between the hub segment 22 and the hub 24, but the alternating arrangement provided by this embodiment also provides a more uniform distribution of the forces across the connect joint 200. Although not shown, it will be appreciated that a similar arrangement of the cross pins 202 and fasteners 204 may couple adjacent hub segments 22 together. In this regard, the connection joint includes a face portion 38a of one hub segment 22 abutting a face portion 38b of an adjacent hub segment 22. The cross pins 202 being inserted in each of the eyes 44 in the adjacent hub segments 22 with U-bolts 206 spanning the connection joint.

[0073] In one aspect of the present invention and with reference to Figs. 2 and 16, the root end 34 of the wind turbine blade 20 may fit over the stem 32 of the hub assembly 22, like a sleeve. As such, the stem 32 extends

longitudinally within the wind turbine blade 20 to a predetermined distance and so produces a region of overlap 300 between the root end 34 and the stem 32. In one embodiment, a pitching mechanism (not shown) may operably couple the wind turbine blade 20 to the hub segment 22 in the region of overlap 300. As shown, the pitching mechanism may include two rotatable joints in the region of overlap 300. In particular, as is shown in Figs. 16 and 16A, a first bearing 302 may be located at or near the root end 34, and a second bearing 304 may be located radially outward therefrom toward the tip 28 of the stem 32. The two bearings 302, 304 are spaced-apart by a distance that may approach or be equal to the length of the region of overlap 300. As can be appreciated, two points of mechanical support as is provided by the two spaced-apart bearings 302, 304 improves the mechanical stability of the coupling between the wind turbine blade 20 and the hub assembly 18. Additionally, the loads applied to the blade 20 are then distributed to both bearings. Thus the loads experienced by any one bearing is reduced (e.g., as compared to a single bearing arrangement). Accordingly, the operating life of the bearing

arrangement should be extended.

[0074] In the exemplary embodiment shown, the first bearing 302 is between the root end 34 of the wind turbine blade 20 and the stem 32 proximate the flared end 30. The wind turbine blade 20 may include a recess 306 proximate the root end 34. The recess 306 includes a bushing 310. As shown, the bushing 310 may project from the recess 306 to sandwich the first bearing 302 between the stem 32 and the bushing 310. Therefore, the bearing 302 may not contact the wind turbine blade 22 directly. By way of example only and not limitation, the bushing 310 may be made of an elastomer, such as rubber, which may be any one or a combination of a variety of synthetic rubbers or a natural rubber. In that regard, the bushing 310 may absorb vibration energy between the wind turbine blade 20 and the hub segment 22, particularly between the root end 34 and the stem 32. Advantageously, this dampening action may improve the dynamic resilience of the hub assembly 18 and the wind turbine blade 20. It will be appreciated that inclusion of an elastomeric bushing is not limited only to the location described above and shown in Fig. 16A. For example, in addition or as an alternative, an elastomeric bushing may be positioned between the second bearing 304 and the wind turbine blade 20 or between either or both of the bearings 302, 304 and the stem 32.

[0075] With continued reference to Fig. 16A, in one embodiment, the bearing 302 includes a tapered outer ring 312. A pair of wedge rings 314, 316 may rest on an inward facing surface of bushing 310 and directly contact each taper on the outer ring 312. As can be appreciated by Fig. 16, forcibly bringing the wedge rings 314, 316 together (according to arrows 320) increases the compression on the bearing 302 between the bushing 310 and the stem 32. This may be achieved, for example, by an adjustable clamp 319 (e.g., bolt and nut). In this way, this rotatable joint may be preloaded. By way of example only, the bearing 302 may be a ball bearing.

[0076] The second bearing 304 is positioned radially outward toward a tip of the wind turbine blade 20 from the first bearing 302. In this sense, the term "radial" denotes a radial direction in relation to the rotor, that is to say, a direction perpendicular to the mainshaft 26, e.g. along a length direction of a blade. In the exemplary embodiment, the second bearing 304 is located at the tip 28. To receive the second bearing 304, the wind turbine blade 20 may include an extension 308 that extends from the inner surface of the wind turbine blade 20 and defines a circular opening 322, a center of which may be coincident with a longitudinal axis of the wind turbine blade 20. The extension 308 fills any out-of-round dimension difference between inside dimension of the wind turbine blade 20 and the circular opening 322 and so may be formed only along one side of the wind turbine blade 22. The extension 308 may provide a platform to which the bearing 304 is secured. In other words, the extension 308 may be a spacer that locates the bearing 304 concentrically with the

longitudinal axis. By way of example only, the bearing 304 may be a ball type bearing. A pitching mechanism (not shown) may then rotate the wind turbine blade 20 relative to the hub segment 22 on the first and second bearings 302, 304 about the longitudinal axis of the wind turbine blade 20.

[0077] To provide axial strength to the bearing connections, a

reinforcement member 330 may be built into the hub assembly 18, for example, in the region of overlap 300. In the exemplary embodiment shown, the reinforcement member 330 may include a cap plate 332 that encloses the tip 28 of the stem 32. The bearing 304 may be coupled to the cap plate 332. A tie rod 334 is secured to the cap plate 332 and extends longitudinally within the stem 32 to a post 336 at or near the hub 24. By way of example, the post 336 may be coupled to each of flanges 46, 48. Alternatively, the post 336 may be positioned within the flared end 30 of the hub segment 22. Axial loads on the wind turbine blade 20 and on the hub segment 22 may be at least partly transferred to the post 336 by the tie rod 334. [0078] While the present invention has been illustrated by a description of various preferred embodiments and while these embodiments have been described in some detail, it is not the intention of the Applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. For example, while the invention has been described in terms of a stud bolt, the invention may be beneficial in applications using other types of bolts or elongated connectors, such as head bolts, etc. Thus, the various features of the invention may be used alone or in any combination depending on the needs and preferences of the user.